We've never had an issue with this before, as all of our customer's open ports, and whitelist domains, as per the Lifesize guides, and port 80 is usually open any/any to begin with.

Recently though we've noticed a couple of instances where the system faced no issues registering and making/receiving calls (so firewall had been configured as per guide), but failed to download the licences; has anyone else reported/noticed this?

We do recommend customers whitelist the *.lifesize.com domain to permit outbound-initiated access via TCP 80 to our cloud servers, but not call security appliances permit this. We don't specifically list the discrete IP address for software.lifesize.com in our reference so this *may* be why it works for some customers (who're less restrictive with their security policies for outbound-initiated connections) but not those to block everything by default.